The modern fuel and ignition system is fully computerized, so each fuel injector or ignition coil will only operate when the onboard computer sends the signal for it to do so. The 1999 Chevy Blazer came with a 4.3-liter V-6 that used a distributor to distribute current to each spark plug, but the computer used the crankshaft position sensor to control rpm and determine exactly when to fire the fuel injectors. Replacing the crankshaft position sensor is a quick job, but you have to perform a relearn procedure before you can drive your vehicle again.

Items you will need

2-ton floor jack

Jack stands

Socket set

Ratchet

Fresh engine oil

Crankshaft position sensor shim

Torque wrench

Wheel chocks

Scan tool with relearn function

Crankshaft Position Sensor Replacement

Step 1

Set the parking brake. Lift the front end into the air, using a 2-ton floor jack, and place place a jack stand under each frame rail. Lower the jack so the Blazer sits on the jack stands.

Step 2

Remove the bolts the hold the skid plate to the bottom of the vehicle, if equipped, using a socket and ratchet. Remove the skid plate.

Step 3

Locate the crankshaft position sensor on the bottom of the engine block, just below the crankshaft pulley. Lift up on the harness locking tab and disconnect it from the crankshaft sensor. Remove the retaining bolt and pull the sensor out of the engine block.

Step 4

Examine the face of the sensor – the part that sits inside the engine – for any gouging. If gouges are present, you must use a shim between the crank sensor and the engine block to prevent damage to the new sensor. Slide a shim over the sensor, if needed, and slide the sensor into the engine block. Install the retaining bolt and tighten it to 15 foot-pounds, using a socket and torque wrench.

Step 5

Plug the wiring harness into the crankshaft sensor. Lift the skid plate into position and install the mounting bolts. Tighten the bolts to 24 foot-pounds. Lower the Blazer to the ground.

Relearn Procedure

Step 1

Place wheel chocks around the rear wheels. Shut the hood and engage the parking brake. Find the data connector under the driver's side dash – it is the same shape as the connector on your scan tool – and connect the scan tool to the connector.

Step 2

Place the transmission in park if your Blazer has an automatic transmission or neutral if equipped with a manual transmission. Start the engine and wait for it to warm up to operating temperature – about 190 degrees, or when the temperature gauge reads about half way. Turn off all accessories like the radio and air conditioning.

Step 3

Turn on the scan tool and enter all the requested information about your Blazer. Scroll to the special functions menu and choose “CKP variation learn procedure.” Slowly raise engine speed to 4,000 rpm. Release the throttle when engine speed begins to drop – this signals the start of the learn procedure. The learn procedure is complete when the scan tool displays “Learn procedure complete,” and you get engine control back. Turn the ignition off for a minimum of 15 seconds, and disconnect the scan tool.

Tip

If you don't have a scan tool with relearn functionality, you can have the vehicle towed to a local shop that can do it for you.